The present invention relates to a method of manufacturing a linear guide device operating as linear guide bearing means and a method of manufacturing a ball screw device, and more particularly to methods of manufacturing a guide rail or a slider body for a linear guide device and to a method of manufacturing a screw shaft and a ball screw nut for a ball screw device, in which their surfaces except the surfaces of parts such as rolling-element rolling grooves and mounting reference surfaces which must be finished with high accuracy, are subjected to rust proofing surface treatment so that the resultant surfaces are completely free from surface damage.
An example of a linear guide device is as shown in FIGS. 8 through 10.
The linear guide device LG provides: a guide rail 1 which is axially elongated; and a slider 2 substantially U-shaped in section which is slidably mounted on the guide rail 1. The guide rail 1 has load ball rolling grooves 3 in its both side surfaces. The surfaces of the load ball rolling grooves 3 are finished by grinding. The slider 2 includes a slider body 2A having a pair of right and left wings 4 and 4. Another load ball rolling grooves 5 are formed in the inner surfaces of the right and left wings 4 and 4 so that they are confronted with the above-described load ball rolling grooves 3. The surfaces of the load ball rolling grooves 5 are also finished by grinding. A number of load balls (not shown) are rollingly fitted in the spaces defined by the opposing load ball rolling grooves 3 and 5. That is, the slider 2 is allowed to slide along the guide rail through the infinite circulation of those load balls.
For the infinite circulation of the load balls, the slider 2 is designed as follows: Through-holes 6 are formed, as ball returning paths, in the right and left wings of the slider body 2A so that they are in parallel with the load ball rolling grooves 5. In addition, U-shaped curved paths (not shown) are form in end caps 2B substantially U-shaped in section which are secured to the front and rear end faces 7 of the slider body 2A, so that the ball rolling grooves 5 are communicated with the ball returning paths 6 through the curved paths thus formed; that is, infinite circulating paths are formed for the load balls. In order to secure the end caps 2B to the front and rear end faces 7 of the slider body 2A with bolts, threaded holes 8 are formed in the front and rear end faces 7 of the slider body 2A.
The linear guide device LG is installed for instance as shown in FIG. 10. The guide rail 1 is fixedly mounted on the machine bed B with bolts, while the slider 2 is fixedly secured to the machine table T with bolts, so that the machine table T is linearly guided. For this installation, mounting bolt holes 9 are formed in the guide rail 1 at intervals which are through-holes extended from the upper surface 1a to the lower surface 1cs; and threaded holes 10 are formed in the four corners of the upper surface of the slider body 2A which are engaged with the mounting bolts.
In setting the linear guide device LG, first the guide rail 1 and the slider 2 of a linear guide device LGs on the reference side are fixed, and adjustment is made with the linear guide device LG on the adjustment side to obtain the necessary mounting accuracy. For this purpose, a mounting reference surface 1cs is formed in the lower surface of the guide rail 1 by grinding which is brought into contact with the mounting reference surface Bs of the machine bed B, and similarly a mounting reference surface 1bs is formed as a part of the side surface 1b of the guide rail 1 by grinding. In addition, a mounting reference surface 2as is formed in the upper surface 1a of the slider body 2A by grinding which is brought into contact with the mounting reference surface Ts of the machine table T, and similarly a mounting reference surface 2bs is formed as a part of the side surface 2b of the slider body 2A.
The accuracies of finishing of the mounting references surfaces 1cs, 1bs, 2as and 2bs of the guide rail 1 and the slider 2 of the linear guide device LGs on the reference side, greatly affect the linear guiding accuracy of the device. Hence, no rust proofing surface treatment is applied to the guide rail 1 and the slider body 2A which are, in general, formed by machining steel, and instead a lubricant containing a rust proofing agent is supplied to the load ball rolling grooves 3 and 5 so that the guide rail and the slider are not only lubricated but also rust-proofed.
On the other hand, an example of a, ball screw device is as shown in FIG. 11.
The ball screw device 100 provides a screw shaft 101 and a ball screw nut 102. Ball rolling grooves 104 are spirally formed in the surface 103 of the screw shaft 101, while ball rolling grooves are formed in the inner surface (not shown) of the ball screw nut 102 so that they are confronted with the aforementioned ball rolling grooves 104. Those ball rolling grooves are finished by grinding. A number of balls are rollingly fitted in the spaces defined by the ball rolling grooves which are confronted with each other. That is, the ball screw nut 102 is moved relative to the screw shaft 101 through the infinite circulation of those balls.
The ball screw device 100 is rotatably mounted on the machine bed B as shown in FIG. 10 with both end portions of the screw shaft 101 supported through bearings. The ball screw nut 102 engaged with the screw shaft 101 is fixedly secured to the lower surface of the machine table T with bolts. Under this condition, the screw shaft 101 is rotated by a driving motor (not shown) so that the machine table T is moved along the linear guide device LG. In the case of the ball screw device 100 too, a lubricant containing a rust proof agent is applied to the ball rolling grooves of the screw shaft 101 and the ball rolling grooves and the ball circulating paths in the ball screw nut 102, so that they are not only lubricated but also rust-proofed.
In the linear guide device LG, the load ball rolling grooves 3 and 5, and the ball returning paths 6 scarcely rust because of being lubricated at all times. Similarly, in the ball screw device 100, the ball rolling grooves 104 of the screw shaft 101, and the ball rolling grooves and the circulating paths of the ball screw nut scarcely rust because of being lubricated at all times. However, the outer surfaces of the guide rail 1 and the slider body 2A, and the outer surface of the ball screw nut 102 are liable to rust due to being not lubricated.
On the other hand, Examined Japanese Patent Publication No. 55515/1990 has disclosed a bearing slider manufacturing method in which a bearing block (corresponding to a slider body) having load ball rolling grooves, ball returning paths and mounting reference surfaces is formed by machining a hardenable steel, and the bearing block thus formed is hardened, and then subjected to black chrome plating to form a protective layer on it, and thereafter mounting reference surfaces and load ball rolling grooves are formed in the bearing block by grinding.
More specifically, in the method of manufacturing the slider of the linear guide device disclosed by the Examined Japanese Patent Publication No. 55515/1990, the slider body in which the load ball rolling grooves, the ball returning paths, the mounting reference surfaces, and the threaded holes have been formed by machining, is subjected to black chrome plating so as to form a rust-proofing layer over all the surfaces of the slider body including the load ball rolling grooves, the ball returning paths, and so forth. Thereafter, the mounting reference surfaces and the load ball rolling grooves which should not be plated from the point of view of operating accuracy, are ground on the grinder. Hence, the method suffers from the following difficulties:
When the slider body is mounted on the grinder, its surfaces other than the mounting reference surfaces and the load ball rolling grooves; that is, the surfaces which should be held covered with the rust-proofing layer may be damaged, or the rust-proofing layers may be peeled off those surfaces, resulting in that the slider body is insufficient in rust prevention.
The surface treatment of the ball screw device 100 is similar to that of the slider body described above. That is, after the ball rolling grooves and the ball circulating paths are formed in the screw shaft and the ball screw nut by machining, a rust-proofing layer is formed over all the surfaces of the screw shaft and the ball screw nut including the ball rolling grooves and the ball circulating paths by plating. Thereafter, the ball rolling grooves which should not be covered with the rust-proofing layer are ground to remove the layer. In this case, similarly as in the above-described linear guide device LG, the surfaces other than the surfaces of the ball rolling grooves may be damaged, or the rust-proofing layers may be peeled off those surfaces, resulting in that the ball screw device is insufficient in rust prevention.